School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemInteractions between fire, environmental heterogeneity and ground-dwelling mammals( 2014)Environmental heterogeneity is known to influence a range of ecological processes at various spatial scales, from individual habitat selection and interspecific interactions, to species’ distributions and diversity. Fire regimes can influence environmental heterogeneity by altering the spatial and temporal distribution of resources. In this thesis I used the ground-dwelling mammals of south-eastern Australia as a focal group to explore the role of fire-mediated heterogeneity in driving individual species distributions, abundance and species diversity. I focussed on two aspects of fire regimes as drivers of environmental heterogeneity at different spatial scales; time since fire at a landscape scale and spatial extent of fire within an individual planned burn. As a secondary objective I also evaluated techniques used to detect ground-dwelling mammals. I investigated relationships between fire-mediated heterogeneity and species diversity at the landscape scale. I compared heterogeneity defined by spatial pattern metrics based on fire age and vegetation type, versus heterogeneity derived from site-based habitat structural measurements. I used two complementary diversity metrics, species richness and beta diversity as response variables. Heterogeneity defined by habitat structural contrasts was positively correlated with beta diversity, however heterogeneity defined by mapped post-fire age classes and vegetation types did not influence beta diversity, and neither measure of heterogeneity was related to species richness. The mammal communities in our study area were influenced by environmental heterogeneity but only if it was present in specific structural attributes of the environment. This suggests that relationships between heterogeneity and diversity depend on how variables representing these properties are quantified. The spatial pattern metrics based on fire age and vegetation type did not reflect physical contrasts that are important for maintaining ground-dwelling mammal diversity. Building on the knowledge at the mammal community level, I investigated individual species responses to time since fire at the landscape scale. Specifically, I used a space for time substitution to investigate interrelationships between the occurrence of eight ground-dwelling mammals, time since fire, and structural resources. Individual species distributions were not well predicted by time since fire. Time since fire was moderately correlated with habitat structure yet was a poor surrogate of mammal occurrence. Variables representing habitat structure were better predictors of mammal occurrence than time since fire for all species considered. These results suggest that time since fire is unlikely to be a useful surrogate for ground-dwelling mammals in heterogeneous landscapes. At a smaller spatial scale, I used a before-after-control-impact experiment, focussed on a planned fire, to investigate the role of unburnt patches in providing post-fire refugia for Agile Antechinus Antechinus agilis and Bush Rats Rattus fuscipes. The two species responded differently to the presence of unburnt patches associated with wet gullies in the burnt landscape. Relative to controls, fire had little effect on Bush Rat abundance in unburnt gullies. In contrast, the fire caused Agile Antechinus abundance to increase in gullies, indicating a shift of individuals from burnt parts of the landscape. Bush Rats that previously occupied burnt parts of the landscape most likely perished in the aftermath of the fire. These differences are likely driven by differences in habitat use and intraspecific competition between these species. I evaluated the three techniques used to detect mammals, live trapping, camera trapping and hair detection. The camera traps detected more species than the other two techniques but live trapping consistently complemented the cameras by detecting unique species. Furthermore the effectiveness of the different techniques varied across the landscape, with live trapping detecting more unique species in wetter, more productive vegetation types, whereas in dry vegetation types the camera trapping alone detected all species present in the sample. I also evaluated two different camera trap models. I found that Reconyx cameras consistently detected more species than Scoutguard camera, mostly because they detected small and medium species more frequently. The results showed that the use of Scoutguard cameras in isolation would have led to erroneous conclusions about the main drivers of species distributions across the landscape.
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ItemThe effects of fire on bark habitats and associated beetle assemblages( 2013)Structurally complex habitats can often support more diverse animal assemblages than simpler habitats. Additionally, changes in habitat structure can alter assemblage composition. Structural changes can occur due to fire, and over time since last fire (TSLF), which may have implications for biodiversity management in fire-prone environments. The bark of Eucalyptus trees is readily modified by fire, but also provides habitat for a diverse fauna, including beetles (order Coleoptera). In a fire-prone forest type in south-east Australia, hypothesised relationships between TSLF, bark complexity and bark-associated beetle assemblages were investigated on two bark types: fibrous bark (typified by Eucalyptus obliqua) and ribbon bark (smooth bark that peels to form loose ‘ribbons’, typified by E. cypellocarpa). The research involved both a long-term (chronosequence ranging from 1 to 72 years postfire) and a short-term component (treatment-control study, comparing sites < 1 year post-fire with sites that had not been burnt for 27 years). Based on ecological theory it was expected that habitat complexity would change with TSLF, and that biodiversity would respond to complexity. The chronosequence study investigated whether bark complexity increased with TSLF; whether beetle richness and Simpson’s diversity relates to bark complexity and/or TSLF; whether TSLF affects assemblage composition; and whether assemblage responses to complexity were stronger than to TSLF. Bark-associated beetles were collected and a range of bark variables were assessed from study trees (of both bark types) at sites belonging four TSLF categories (1- 5 years; 27 – 29 years; 43 – 49 years; 72 years). Several aspects of bark complexity on fibrous-barked trees related to TSLF, but none on ribbon-barked trees. On fibrous-barked trees, Simpson’s diversity (but not richness) correlated modestly with the one element of bark complexity (surface cover of loose bark flaps), but with no others, nor with TSLF. On ribbon-barked trees, richness (but not Simpson’s diversity) was modestly related to the surface cover of loose ‘ribbons’. No other relationships with bark complexity or TSLF were found. On neither bark type was a TSLF effect on assemblage composition apparent; with many common morphospecies detectable throughout the chronosequence. Composition did not differ between the two bark types, and many morphospecies used both, suggesting that many beetles in this system can tolerate substantial differences in bark structure. The short-term comparative study was adopted in order to clarify the effects of very recent fire on bark complexity, and because some fire effects on beetle assemblages were anticipated to be short-lived (< 1 year). Burnt sites were found to have less complex bark than unburnt sites, and differences in assemblage composition (but not richness or Simpson’s diversity) were detected. Despite the detection of short-term compositional differences, the lack of longer term differences, and paucity of strong relationships with complexity, suggested that these assemblages were resilient, rather than responsive, to fire-related habitat change. This was contrary to hypothesised relationships between structural complexity and biodiversity, but consistent with suggestions that assemblages in fire-prone regions will exhibit a degree of resilience to fire impacts.